Pauli comments Spizer's paper on "Communication relations of interacting spinor fields" published in: Phys. Rev. : 105 (1957), pp. 1919.

Pauli encloses a letter by Heisenberg and asks Källén to write to him.

Pauli expresses his doubts whether Källén's mathematics has anything to do with physics. He talks about Heisenberg's approach to the problem of field theory.

Pauli talks about the progress made by Taylor in Princeton and Bogoljubov in dispersion relations and he writes about the article for the Springer Handbuch.

Pauli writes on calculations and remarks about interactions in which P and T are coupled. Pauli's new mathematical approach proves violation of P-invariance and T-invariance for certain cases.

Pauli asks questions about the non-occurence of $\pi \to e+v$ and $\pi e+v+photon$. He talks about Heisenberg's work and his idea that the real world results from a bi-section of a $\gamma$-invariant world, for non-zero rest mass and for the neutrino a leptonic charge.

Pauli clarifies additions to the last letter. On the CTP-theorem and the idea of regarding antiparticles as mirror images of particles.

Pauli writes on the significance of the case of the double root in quantized field theory.

Pauli discusses Heisenberg's formulae in his letter of the 13 September 1957.

Pauli asks questions about the reactions $\pi \to \mu + \nu$ and $\pi e + \nu$. He comments papers by Sakurai and Havana (in: Progr. Theor. Phys. : 17 (1957), pp.592).